A bit of simple code to enable the full ES Internationalization API in Chrome 21+. Does not work in Chrome Canary.

index.html

<h1>Examples</h1>
  

script.js

(function(window) {
    //check for V8 implementation support in Chrome
    if ('v8Intl' in window) {
        //We may need to rewrite the standard functions to use the Intl formatters
        var oldToLocaleDateString,
            oldNumberToLocaleString,
            oldToLocaleTimeString,

            //we check if various API calls are supported using this date
            date = new Date('1/1/2001');

            //property used in testing if 18n API is already implemented
            props = {
                weekday: 'long',
                timeZoneName: 'long' 
            };

        //create a proxy;
        window.Intl = v8Intl;

        //Check if toLocaleDateString already supported 
        if (date.toLocaleDateString(['en'], props) !== 'Monday') {
            oldToLocaleDateString = Date.prototype.toLocaleDateString;
            Date.prototype.toLocaleDateString = function(locales, options) {
                var formatter;
                if (locales === undefined && options === undefined) {
                    return oldToLocaleDateString.call(this);
                }

                //clean up and normalize;
                locales = String(locales).split(',');
                options = Object(options);

                //format and return result;
                formatter = new window.Intl.DateTimeFormat(locales, options);
                return formatter.format(this);
            }
        }

        //check Time Formatting support
        if(date.toLocaleTimeString(["en"], props) !== "12:00:00 AM GMT+00:00"){
            oldToLocaleTimeString = Date.prototype.toLocaleTimeString;

            Date.prototype.toLocaleTimeString = function(locales, options) {
                var formatter, defaults;
                if (locales === undefined && options === undefined) {
                    return oldToLocaleTimeString.call(this);
                }

                //clean up and normalize
                locales = String(locales).split(',');
                options = Object(options);

                //set defaults for output, as Chrome does not do this
                defaults = ['hour', 'minute', 'second'];
                for (var i = 0; i < defaults.length; i++) {
                    if (!(defaults[i] in options)) {
                        options[defaults[i]] = 'numeric';
                    }
                }

                //format and return result;
                formatter = new window.Intl.DateTimeFormat(locales, options);
                return formatter.format(this);
            }
        }

        //check number formatting support
        if((123456).toLocaleString(["en"]) !== "123,456"){
            oldNumberToLocaleString = Number.prototype.toLocaleString;
            Number.prototype.toLocaleString = function(locales, options) {
                var formatter;
                if (locales === undefined && options === undefined) {
                    return oldNumberToLocaleString.call(this);
                }

                //clean up and normalize;
                locales = String(locales).split(',');
                options = Object(options);

                //format and return result;
                formatter = new window.Intl.NumberFormat(locales, options);
                return formatter.format(this);
            }
        }
    }
})(window);


//Show examples
var date = new Date('1/1/2001'),
    options = {
        weekday: 'long'
    };
var elem = document.createElement("div"); 
 
elem.innerHTML += "toLocaleDateString: " + date.toLocaleDateString() + "<br>"; 
elem.innerHTML += "toLocaleTimeString: " + date.toLocaleTimeString() + "<br>"; 
elem.innerHTML += "Weekday 'en': " + date.toLocaleDateString('en', options) + "<br>"; 
elem.innerHTML += "Weekday and time 'pt': " + date.toLocaleTimeString('pt', options) + "<br>"; 
elem.innerHTML += "Chinese Time: " + date.toLocaleTimeString('zh') + "<br>"; 

var number = 123456789;
elem.innerHTML += "toLocaleString of number: " + number.toLocaleString() + "<br>";
elem.innerHTML += "Number formatted for Portgal: " + number.toLocaleString('pt-PT')  + "<br>";
elem.innerHTML += "Number formatted for Brazil: " + number.toLocaleString('pt-BR')  + "<br>";
elem.innerHTML += "Number formatted for English: " + number.toLocaleString('en', {})  + "<br>";
document.body.appendChild(elem);